The present invention relates to medical imaging and more specifically magnetic resonance imaging (MRI).
Various neuroimaging techniques are presently available. These techniques include MRI, functional MRI (fMRI), and positron emission tomography (PET), for example. None of these techniques, however, are able to directly measure neural activity, i.e., brain activity.
Instead, these techniques detect brain activity via cerebral hemodynamic and metabolic responses to neural firing. However the temporal resolutions of fMRI and PET are ultimately limited by the slow response function of cerebral hemodynamics, which is on the order of seconds. Furthermore, their inferences regarding neuronal activity are necessarily complicated by the variability of coupling between neuronal activity, cerebral hemodynamics, and metabolism.
Other techniques to map neural activity include electroencephalography (EEG) and/or magnetoencephalography (MEG). However, these techniques often have poor spatial resolution. Because both EEG and MEG rely on information detected at the scalp to localize active sites inside the brain, both EEG and MEG require solving an inverse problem, which leads to spatial uncertainty in the localization of electromagnetic sources. In addition, EEG and MEG are each limited in the activation geometries they can detect and are unable to detect neuronal activities deep in the brain. While combining information from modalities detecting different physiological variables (for example, data from fMRI and MEG) can partially offset the drawbacks of the individual modalities and can provide brain activation maps with high spatial and temporal resolution, the basic limitations for each modality, such as the indirect nature of fMRI measurement and the inverse problems for EEG and MEG, remain obstacles.
Thus a need exists to provide improved combined spatio-temporal resolution of neural activity imaging. Further, a need exists to directly map such neural activity to avoid the inverse problem, and directly measure magnetic sources originating from neural firing with high spatio-temporal resolution.